1. Field of the Invention
This invention relates to imaging in optical code reading devices. Aspects of the invention are particularly useful in solid-state optical code readers for illuminating and imaging remote target indicia, such as an optical code. The present invention is useful in CCD based bar code readers, and other imaging devices.
2. Description of the Related Art
Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term “barcode” is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as “optical code readers” of which barcode scanners are one type. Optical code readers are used in fixed or portable installations in many diverse environments such as in stores for checkout services, in manufacturing locations for workflow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target barcode from a printed listing of many barcodes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a handheld sensor that is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional barcode symbols. The barcode is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one-dimensional barcode is the UPC/EAN code used to identify, for example, product inventory. An example of a two-dimensional or stacked barcode is the PDF417 barcode. A description of PDF417 barcode and techniques for decoding it are disclosed in U.S. Pat. No. 5,635,697 to Shellhammer et al., and assigned to Symbol Technologies, Inc., which is incorporated herein by reference. Another conventional optical code is known as “MaxiCode.” It consists of a central finder pattern or bull's eye center and a grid of hexagons surrounding the central finder. It should be noted that the aspects of the inventions disclosed in this patent application are applicable to optical code readers, in general, without regard to the particular type of optical codes, which they are adapted to read. The invention described may also be applicable to some associated image recognition or analysis.
Most conventional laser scanning systems generate one or more beams of laser light, which reflects off a barcode symbol, and back to the scanning system. The system obtains a continuous analog waveform corresponding to the light reflected by the code along one or more scan lines of the system. The system then decodes the waveform to extract information from the barcode. A system of this general type is disclosed, for example, in U.S. Pat. No. 4,251,798, assigned to Symbol Technologies, Inc. A beam scanning system for detecting and decoding one and two-dimensional barcodes is disclosed in U.S. Pat. No. 5,561,283 also assigned to Symbol Technologies, Inc.
Typically, a laser beam generated by a laser source, for example, a gas laser tube or a semiconductor laser diode, is optically focused by an optical train into a generally circular laser beam spot on a symbol. The beam spot is swept by a scanning component over the symbol and forms a scan pattern thereon. Laser light reflected off the symbol is detected by a light sensor, e.g. a photodiode, mounted together with the laser source, the optical train, the scanning component, and the photodiode in a housing, preferably one having a handle to enable hand-held, portable operation.
The symbol itself is a coded pattern comprised of a series of bars of various widths, the bars being spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflective properties. Although dimensions may vary, depending on the particular application and the density of the symbol, each bar and space of a UPC symbol typically used in the retail industry to identify retail products measures on the order of thousandths of an inch (mils). In practice, the generally circular laser beam spot has a cross-sectional diameter on the order of 6 to 10 mils.
Barcodes can also be read by employing imaging systems having an image sensor and a plurality of illuminating devices for illuminating the field of view. The image sensor generally includes a two-dimensional array of cells or photo sensors which correspond to image elements or pixels in the field of view. The image sensor may be a two-dimensional or area charge coupled device (CCD) and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view.
Laser scanning and imaging systems generally include a handheld unit that is manually pointed at the target during a scanning or imaging procedure. The handheld unit is often a component of a much larger system including other scanners, computers, cabling, data terminals, etc, Such systems are frequently designed and constructed based on mechanical and optical specifications for the scanning engine, sometimes called “form factors.” One such form factor is the SE900 form factor utilized by Symbol Technologies, Inc. Accordingly, there is a need to provide a compact imaging engine that can be substituted for conventional laser line scanning engines in currently designed and currently deployed optical code reader systems.
There is another need to provide an imaging engine that can be substituted for predetermined form factor scanning engines, such as the SE900 form factor scanning engine, in currently designed and currently deployed optical code reading systems to increase the reliability, versatility, and target working range of such systems.